1. Field of the Invention
The present invention relates to friction devices such as clutch or brake assemblies for use in transmissions, differentials or brake systems and more particularly to such devices having a piston actuated clutch or brake pack including separator plates and friction discs.
2. Description of the Prior Art
The transmission mechanism described here includes a hydrokinetic torque converter having a bladed impeller driven by an internal combustion engine for an automotive vehicle. The converter includes also a bladed turbine and a bladed stator situated in toroidal fluid flow relationship with respect to the impeller. The turbine is connected to torque input elements of a multi-speed ratio planetary gear system. The output portion of the gear system is connected to a transmission tailshaft, which in turn is connected to the vehicle traction wheels through a driveshaft and differential-and-axle assembly.
The reaction element for the gear system is adapted to be anchored by the improved friction disc coupling of the present invention. Such braking action is useful in for holding a component of a gear set during a particular gear range. In certain applications it is know to employ several multi-disc pack friction devices in combination to establish different drive connections throughout the transmission or differential to provide various gear ratios in operation or to brake a component.
In certain prior art mechanisms the engagement of an underdrive speed ratio band brake is accompanied by an undesirable harshness due to the sudden application of friction braking torque. Attempts have been made to cushion the engagement of the friction brake bands in environments of this type, one arrangement being shown in Duffy U.S. Pat. No. 3,004,390 and another arrangement is shown in U.S. Pat. No. 2,633,712. U.S. Pat. No. 3,693,800 sets forth a cushioning action in a friction disc brake, as distinguished from a band brake, and it provides an accumulator action following initial cushioned engagement of the friction discs as the mechanism is conditioned for underdrive operation. The cushioning action that occurs during initial braking engagement provides a reduced or modified torque capacity. This is followed by stroking of the main piston portion of the mechanism. As an accumulating action takes place, the portion of the compound piston structure that establishes the initial braking engagement cooperates with the main piston portion to define a common working chamber. As the main piston portion moves with respect to the smaller piston portion, an accumulator action takes place because of the compression of a piston spring acting on the main piston portion.
After the main piston portion moves relative to the smaller piston portion to its limiting position, the brake servo pressure rises to its maximum value, thereby establishing full braking action. At that instant motion of the reaction element relative to the stationary transmission housing will approach zero angular velocity.
Timing orifices may be formed in the main piston portion. The size of the orifices, as well as the characteristics of the spring acting on the main piston portion, may be varied to suit particular design characteristics.
While suitable for their intended purpose, such arrangements fail to provide an easily assembled friction disc coupling that can be accommodated in a limited radial space between a torque converter and a transmission for a front wheel drive vehicle.